1. Field of the Invention
This invention is directed to MOS semiconductor devices, in general, and to such devices which have extraordinarily small dimensions and the methods of making such devices, in particular.
2. Prior Art
There are many known techniques and processes for making semiconductor devices of many and varied types. Many of these devices which are fabricated are of the so-called "N-channel" variety. Many of the known processes include E-beam lithography, X-ray lithography, dry processing techniques or wet processing techniques. The types of processing which are utilized are a function of the device to be fabricated and the size thereof. For example, dry processing techniques permit more vertically arranged device edges and the like so that dimensions can be reduced.
Semiconductor devices having dimensions on the order of 1 to 2 microns are known in the art. However, in order to produce very large scale integrated (VLSI) devices and techniques, the existing technologies have been studied extensively to establish methods of reducing the size of the MOS transistor. In theory, reducing the size of an MOS transistor is straightforward. However, this size reduction cannot easily be accomplished inasmuch as it requires maintaining the same relative characteristics and threshold voltage after scaling so that the same circuit design can serve for both small and large geometries. While this reduction in size is, theoretically, straight-forward, many factors must be taken into consideration. Moreover, theoretical predictions by computer simulation, for short channel, narrow gate width devices is not as easily converted into actual practice as initially thought. Many process and device parameters must be scaled down concurrently to produce a useful device and to avoid undesirable side effects. Thus, it is essential that the appropriate combination of techniques, most of which are standard or known in the art, be established in order to optimize the processing techniques and, thus, minimize the size of the various semiconductor devices.